Folding bicycles are becoming more and more popular. Nowadays, most folding bicycles are provided with a folding joint on the beam, such that the beam can be folded into two segments when not in use. When in use, the front segment and the rear segment of the beam are locked through a locking device on the folding joint. The folding joints, which are disclosed in Chinese patents CN200420093887.5 and CN01255435.9, are common ones widely used in bicycles. Chinese patent CN00260163.X, whose applicant is the same as the present invention, discloses a reinforced mechanism of folding joint of single beam folding bicycle; and in the second embodiment of the patent, a reinforcing arm, which is connected with the beam and the seat tube, is provided, but only to reinforce the beam, while the original folding joint and the locking device for the folding bicycle are still necessary, and an additional fixing seat should be provided on the seat tube; when the folding bicycle is in normal use, following steps are necessary: locking the folding joint of the beam, locking the clamping ring for the seat tube, and buckling the reinforced mechanism to the fixing seat of the seat tube, as a result, too many steps are needed, it is inconvenient for use and the bicycle can't be unfolded or folded quickly.
Moreover, the Chinese patent application No. 200510025883.2 discloses a folding bicycle, as shown FIG. 1, the folding bicycle can be folded in a direction parallel to the plane of the front hub and the rear hub. The hinge axle is provided horizontally, and the opening of the folding joint faces upward. The folding joint is provided with a pivot 211, which is provided with a connecting bar 2. The connecting bar is connected to the C-shaped ring 22 and is locked horizontally. After the connecting bar 2 and the hook 213 are locked, there are no horizontal displacements relative to their original position. The defects of this scheme are as follows: no pre-tightening force is exerted on the connecting bar 2 in the direction along which the folding joint is buckled, as a result, when the connecting bar 2 moves upwards due to the rough road or other impacts in cycling, the beam will break, which will bring great potential safety risks. When the connecting bar 2 moves upwards, the resistant force exerted on the connecting bar is only the frictional force generated by locking horizontally, which makes the margin of safety extremely thin. Moreover, the pivot 211 is provided on the contacting surfaces on the front frame, so the effect of locking on the contacting surfaces on the front frame is rather limited. Moreover, when in cycling, the C-shaped ring 22 is loose and apt to slide along the seat tube, which will cause the connecting bar 2 loose and will bring unsafe factor.
How to improve the strength of the beam and unfold or fold the bicycle with fewer steps has become an urgent problem to be solved.